Agrobacterium tumefaciens is a well-known plant pathogen, but has only recently been recognized as an opportunistic pathogen of humans. More information is needed to understand how the bacterium can be such a broad range pathogen, both for understanding its basic biology and to provide possible targets for future control of human infection. The specific goals of this proposal are 1) to functionally characterize two recently discovered genes that have strong homology to known virulence or interaction determinants in other organisms, 2) to determine if A. tumefaciens really contains a remnant of an animal-specific virus in its genome as a "footprint" of a past animal infection event, 3) sequence about10 percent of the A. tumefaciens genome in order to search new genes involved in virulence or interaction, and 4) to functionally characterize a few of these new genes. Both biochemical and genetic approaches will be used to test gene functions.